Prototype optical atomic clock in a
PTB quantum optics laboratory.
The instrument will be at least 100x
as accurate as present-day ceasium
atomic clocks and may one day
serve as a better primary standard
of frequency.
The oscillation of a selected atomic
transition of 10 million strontium
atoms trapped inside a spherical
vacuum chamber is used as a pace-
maker of unrivalled accuracy.

[s] ‘The SECOND is the duration
of 9 192 631 770 periods of the
radiation corresponding to the
transition between the two hyperfine
levels of the ground state of the
caesium 133 atom.’